ftp.nice.ch/peanuts/GeneralData/Documents/books/AlexNeXTSTEPSource.tar.gz#/NSProgramming/Chapter3_OOD/ShapeArea/Square.m

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#import "Square.h"

@implementation Square

// override method to print the width and height
// as well as the area
-(float)calcArea
{
	// use self to refer to the same object
	// that received the calcArea method
	[self printHeight];
	[self printWidth];
	// use super to access the superclass'
	// implementation
	return [super calcArea];
}

-printHeight
{
	printf("The height is %.2f\n", height);
	return self;
}

-printWidth
{
	printf("The width is %.2f\n", width);
	return self;
}

-free
{
	return [super free];
}

@end

These are the contents of the former NiCE NeXT User Group NeXTSTEP/OpenStep software archive, currently hosted by Netfuture.ch.